For semiconductor device products, a plurality of times of exposure processes are required to form a circuit pattern required for operation. For example, in manufacture of a device formed of multilayered circuit patterns, in addition to the exposure process for forming each layer of the circuit pattern, an exposure process for forming a hole connecting together the layers is required. Position of the circuit patterns formed through the aforementioned plurality of times of exposure processes needs to fall within a permitted range, and upon deviation from the permitted range, appropriate electric characteristics cannot be obtained, resulting in yield deterioration. Thus, measurement of circuit pattern misalignment (overlay) between the exposures and feedback thereof to an exposure device have been practiced.
Following miniaturization of semiconductor processes, the permitted overlay range has become smaller and thus has become important to directly measure the overlay in a place where the product circuit pattern is formed. To realize this, Japanese Patent Application Laid-open No. 2013-168595 (Patent Literature 1) describes a technique of photographing an image of a product circuit pattern with a scanning electron microscope (SEM) and measuring overlay.
The overlay measurement method described in Patent Literature 1 measures the overlay through image positional alignment between a reference image and a measured image, and FIG. 30 in Patent Literature 1 describes a method of providing a display of measurement results as detection results of a differential part between the reference image and the measured image.
Japanese Unexamined Patent Application Publication No. 2005-521254 describes a method of coloring a reference image and an inspected image to make a difference therebetween visible. More specifically, the method refers to an inspection method of image comparison between the reference image and the inspected image and a method of obtaining an inspected defective image by image coupling of a framework image of the colored reference image, an edge framework image of the colored reference image, and an inspected object of the colored inspected image.